Current actuators are widely used in intelligent furniture such as an electric sofa and an electric bed, and also used in electric telescoping devices in hospital such as a medical bed and a dental chair. However, when specific devices such as the electric sofa, the electric bed, the medical bed and the dental chair use bidirectional (with thrust and pull force) actuators, pull strength thereof is powerful, hands and legs of a user will be easy to be crushed or even broke and an accident will occur by the slightest carelessness when the actuator is pulled back. Therefore, these specific devices can only utilize unidirectional (only with thrust force) actuators. Since the actuator only has unidirectional thrust force, devices such as the electric sofa, the electric bed, the medical bed and the dental chair have no self-returning function after they are pushed out, and only external force applied by a person can reposition the devices.